This invention relates generally to manual exercisers suitable for athletic or therapeutic purposes, and more particularly to an isokinetic exerciser in the form of a push-pull hydraulic device provided with a pair of handle pieces and requiring an evenly applied muscular force to effect compression or expansion.
In contemporary society, large-scale mechanization has sharply reduced the need for an expenditure of physical energy in the production of goods and services. Indeed, the aim of most inventions is to provide a labor-saving device to supplant human effort. But while modern man has been relieved of the Biblical injunction to earn his daily bread by the sweat of his brow, this has been a mixed blessing; for the resultant inactivity has given rise in affluent societies to serious obesity problems and has impaired the ability of many persons to carry out their normal tasks with a reasonable degree of efficiency.
To remediate many of the physical fitness problems of the sedentary individual, various forms of exercisers have been contrived that are designed to develop muscular strength and endurance. By muscular strength is meant the measurable strength of muscles as determined by a single maximum contraction, and by muscular endurance is meant the ability of muscles to perform work for a given time period.
Most exercisers in current use fall either into the isometric or isotonic class. An isometric exerciser is designed to sustain one muscular contraction and therefore operates on static tension, whereas an isotonic exerciser adapted to repeatedly raise or lower a weight or other load brings into play dynamic tension.
In a review by the President's Council on Physical Fitness and Sports of the research carried out on the comparative effects of isometric and isotonic training programs, as reported in the Physical Fitness Research Digest of Jan. 1974 (Series 4, No. 1), the Council indicated a preference for the isotonic over the isometric form and concluded that isotonic training is superior in developing muscular strength and in improving muscular endurance. The Council pointed out that motiviation is greater in isotonic exercising, for the participant can see what is being accomplished and explicit goals may be set. This does not mean that isometric exercising is less valuable, for it is useful in developing muscular strength in circumstances which preclude isotonic training.
But from the standpoint of overall physical fitness enhancement, neither isotonic nor isometric forms of exercise are adequate, for these exercises fail to contribute in any appreciable degree to the improvement of circulatory-respiratory endurance, an important aspect of well-being.
In recent years, a third training technique has been developed by experts in the physiology of exercise and physical therapy to improve overall physical fitness. This new technique, which combines the best attributes of isotonic and isometric training, has been designated isokinetic training. In isokinetic exercise, maximum dynamic tension is developed throughout a range of motion.
When performing isotonic or isometric exercises, strength development is not achieved equally throughout the range of motion. In isotonic exercise, the magnitude of isotonic resistance must be limited to the largest load that can be moved at the weakest point in some range of motion. This resistance will therefore be less than maximum during the rest of the range and thus will not load the muscle to its full tension-developing capacity in much of its shortening range. Moreover, in isotonic training, the exercise speed is subject to considerable acceleration and is therefore unstable and unpredictable.
On the other hand, isometric exercise takes place against a load which prevents external movement and offers resistance inherently proportional to the muscle's static tension-developing capacity at one shortening length. No dynamic work at all is carried out; hence the intrafiber power developed is inherently restricted.
The present invention, which operates on isokinetic principles, constitutes an improvement over the hydraulic double-acting exerciser disclosed in applicant's prior U.S. Pat. No. 3,834,696. In this prior exerciser, handles are attached to the ends of a hydraulic bar formed by inner and outer telescoping tubes in an arrangement in which the handles are attached to bolts extending from the ends of the tubes so that the handles are spaced from the ends. As a consequence, the ends of the tubes are unprotected, and, in practice, the clothing of the user may be caught in the spaces between the handles and the tube ends.